1. Field of the Invention
This invention relates to a detecting apparatus for abnormality in an inverter circuit which detects abnormality in operation of an apparatus which performs conversion of electric power by using inverters such as no-break power units.
2. Description of the Prior Art
FIG. 1 is a circuit diagram showing an example of a conventional detecting apparatus for abnormality in an inverter shown in, for example, Japanese Patent Laid-open No. 53-88121 (1978). In FIG. 1, a numeral 1 shows a three-phase auxiliary pulse commutating inverter circuit, a numeral 2 a DC power source, a numeral 3 a high speed breaker, a numeral 4 a current limiting reactor, a numeral 5 a balanced capacitor, a numeral 6 an auxiliary thyristor arm, a numeral 7 an insulating transformer, a numeral 8 a rectifier, a numeral 9 a transistor, numerals 10 and 11 are NOT circuits, a numeral 12 is an exclusive OR circuit, a numeral 13 a monostable multivibrator, and a numeral 14 a commutation detecting circuit. FIG. 2 is a time chart explanatory of operation of the conventional example.
Next, the operation of the conventional example will be described.
When the three-phase auxiliary pulse commutating inverter circuit 1 operates normally, a pulse voltage appears with a commutation period at the output of the insulating transformer 7 connected between the center of capacitors 5A and 5B composing the balanced capacitor 5 and that of auxiliary thyristor arms 6A and 6B composing the thyristor arm 6 of the inverter 1, the pulse voltage is input to the commutation detecting circuit 14 via the rectifier 8, and the input waveform becomes as shown in the period T.sub.1 in FIG. 2(a). On the other hand, a command pulse waveform for commutation in the inverter as shown in the period T.sub.1 in FIG. 2(b) is applied to the commutation detecting circuit 14 from a control circuit (not shown). A transistor 9 repeats on-off action depending upon an input from the insulating transformer 7 and obtains a waveform as shown in the period T.sub.1 in FIG. 2(c) as a collector output. Furthermore, the waveform is inverted by the NOT circuit to obtain a waveform as shown in the period T.sub.1 in FIG. 2(d) having the same phase as the command pulse waveform for commutation shown in the period T.sub.1 in FIG. 2(b). The command pulse waveforms for commutation shown in FIG. 2(b) are input from the NOT circuit and the control circuit into the exclusive OR circuit 12, which outputs "0" outputs in succession at the logic at which both inputs are "0" or "1", and a waveform shown in the period T.sub.1 in FIG. 2(e) is obtained. The monostable multivibrator 13 outputs "1" of the waveform shown in the period T.sub.1 in FIG. 2(f) in succession, and "0" of a waveform shown in the period T.sub.1 in FIG. 2(g) is obtained as an output of the NOT circuit 11. On the other hand, when commutation in the inverter becomes abnormal, a waveform "1" shown in the period T.sub.2 in FIG. 2(g) is obtained as an output of the NOT circuit 11 as shown by the waveforms shown in the period T.sub.2 in FIG. 2(a) through (g), thereby detecting abnormality.
Since a conventional detecting apparatus for abnormality in an inverter had such a constitution that the insulating transformer 7 was directly connected between the center of the capacitors 5A and 5B composing the balanced capacitor 5 and that of the auxiliary thyristor arms 6A and 6B composing the auxiliary thyristor arm 6, the insulating transformer 7 needed an iron core of sufficient size to have a capacity of magnetic flux in accordance with the commutation period and, in addition, iron cores of at least the same number as that of the auxiliary thyristor arms 6 were employed. There was, therefore, a problem that the whole of the inverter apparatus became large in size and heavy in weight. In addition, there was a problem that instability in operation because of erroneous detection of abnormality confirming operation and the like occurred due to delay in operation of switching elements in the main circuit and element driving circuits.